a memory; and

at least one processor connected to the memory, the at least one processor configured to:

determine a prediction mode as an inter prediction mode to be used for a block;

determine one transform configuration group of a plurality of transform configuration groups to be used for the block of the inter prediction mode, wherein each of the plurality of transform configuration groups includes a plurality of transform combinations;

obtain a transform index, wherein the transform index (i) indicates one of a plurality of transform combinations of the determined one transform configuration group of the plurality of transform configuration groups, (ii) is a single transform index corresponding to a first index value for a horizontal transform and a second index value for a vertical transform, and (iii) is comprised of values of 0, 1, 2, 3, 4, and wherein the first index value and the second index value are determined based on the transform index and the one transform configuration group;

derive a transform combination corresponding to the transform index, wherein the transform combination is configured with a horizontal transform and a vertical transform and includes one of (DST (Discrete Sine Transform)-7, DST-7), (DST-7, DCT (Discrete Cosine Transform)-8), (DCT-8, DST-7) and (DCT-8, DCT-8);

perform an inverse transform on a transform unit based on the transform combination; and

reconstruct the video signal based on the transform unit.